Comparative genomic analysis of the tailed bacteriophages shows that they are genetically mosaic with respect to each other, implying that horizontal exchange of sequences is an important component ...of their evolution. Horizontal exchange occurs intensively among closely related phages but also at reduced frequency across the entire population of tailed phages. It results in exchange of homologous functions, exchange of analogous but non-homologous functions as with the prophage integrases, and introduction of novel functions into the genome as with the morons. Extrapolation of these processes back in evolutionary time leads to a speculative model for the origins and early evolution of phages.
We present detailed photometric properties of the Moon at far ultraviolet wavelengths. The far ultraviolet data from the Lunar Reconnaissance Orbiter (LRO) Lyman Alpha Mapping Project (LAMP) ...instrument were used to derive two Hapke photometric parameters, the single‐scattering albedo, w, and the asymmetry factor, b, in the single‐particle phase function, for selected mare and highland regions. The derived single‐scattering albedo spectra show blue slopes for both regions. Furthermore, the negative values of the asymmetry parameter, for both regions, indicate backscattering from the surface. The derived photometric parameters were used to normalize the observed reflectance and remove the photometric effects, resulting in significant improvement in the quality of the LAMP dayside maps.
Plain Language Summary
The photometry of the Moon gives us much information about the optical properties (i.e., brightness and color) of lunar surface. Using the data from an instrument called Lyman Alpha Mapping Project onboard the Lunar Reconnaissance Orbiter, we studied the detailed photometric properties of the two regions (selected mare and highland regions) on the Moon at far ultraviolet wavelengths. We used an empirical model called Hapke model to describe the surface reflectance at far ultraviolet wavelengths and then used the model to fit the curves of the reflectance as a function of phase angle (angle between direction of incoming sunlight and the direction of reflected sunlight toward the observer). The fitting process gives the Hapke parameters, which can be used to correct the photometric effects on the data due to the varying viewing geometries. Our corrections result in significantly improved Lyman Alpha Mapping Project reflectance maps.
Key Points
Phase curves at far ultraviolet wavelengths over selected mare and highlands regions of the Moon were investigated with LRO LAMP data
Two Hapke photometric parameters, the single‐scattering albedo, w, and the asymmetry factor, b, were derived with a simplified Hapke model
Photometric correction using the derived Hapke parameters has significantly improved the quality of the LAMP dayside maps
•Experiments for by-pass pigging under low pressure conditions have been performed.•Oscillatory behaviour of the pig motion has been described by a simplified model.•A controller which actively ...regulates the by-pass can suppress pig velocity excursions.
We present experimental and numerical results for by-pass pigging under low-pressure conditions which aided the design of a speed-controlled pig (Pipeline Inspection Gauge). Our study was carried out using air as working fluid at atmospheric pressure in a 52 mm diameter pipe of 62 m length. The experimental results have been used to validate simplified 1D models commonly used in the oil and gas industry to model transient pig behaviour. Due to the low pressure conditions oscillatory behavior is observed in the pig speed, which results in high pig velocity excursions. The oscillatory motion is described with a simplified model which is used to design a simple controller aimed at minimizing these oscillations. The controller relies on dynamically adjusting the by-pass area, which allows to release part of the excess pressure which builds up in the gas pocket upstream of the pig when the motion of the pig is arrested. Subsequently, the control algorithm is tested by a 1D transient numerical model and it was shown to successfully reduce the pig velocity excursions.
Unbalanced actions of the quadriceps components are closely linked to patellar mal-tracking and patellofemoral pain syndrome. However, it is not clear how individual quadriceps components pull and ...rotate the patella three dimensionally. The purpose of this study was to investigate in vivo and noninvasively patellar tracking induced by individual quadriceps components.
Individual quadriceps component was activated selectively through electrical stimulation at the muscle motor point, and the resulting patellar tracking was measured in vivo and noninvasively in 18 knees of 12 subjects. The in vivo and noninvasively patellar tracking was corroborated with in vivo fluoroscopy and in vitro cadaver measurements.
Vastus medialis (VM) mainly pulled the patella first in the medial and second in the proximal directions and vastus lateralis (VL) pulled first in the proximal and second in the lateral directions. The oblique portion (VMO) of the VM pulled the patella mainly medially and the longus portion (VML) more proximally. Medial tilt was the major patellar rotation induced by VMO contraction at full knee extension. With the knee at the more flexed positions, the amplitude of patellar movement induced by comparable quadriceps contractions was reduced significantly compared to that at full knee extension, and VMO changed its main action from extending to flexing the patella.
The medial and lateral quadriceps components moved the patella in rather different directions, and rotated the patella differently about the mediolateral tilt and mediolateral rotation axes but similarly in extension. The approach can be used to investigate patellar tracking in vivo and noninvasively in both healthy subjects and patients with patellofemoral disorder and patellar malalignment.
The bacteriophage HK97 capsid is a molecular machine that exhibits large-scale conformational rearrangements of its 420 identical protein subunits during capsid maturation. Immature empty capsids, ...termed Prohead II, assemble in vivo in an
Escherichia coli expression system. Maturation of these particles may be induced in vitro, converting them into Head II capsids that are indistinguishable in conformation from the capsid of an infectious phage particle. One method of in vitro maturation requires acidification to drive the reaction through two expansion intermediates (EI-I, EI-II) to its penultimate particle state (EI-III), which has 86% more internal volume than Prohead II. Neutralization of EI-III produces the fully mature capsid, Head II. The three expansion intermediates and the acid expansion pathway were characterized by cryo-EM analysis and 3D reconstruction. We now report that, although large-scale structural changes are involved, the electron density maps for these intermediate states are readily interpreted in terms of quasi-atomic models based on subunit structures determined by prior crystallographic analysis of Head II. Progression through the expansion intermediate states primarily represents rigid-body rotations and translations of the subunits, accompanied by refolding of two small regions, the N-terminal arm and a β-hairpin called the E-loop. Movies made with these pseudo-atomic coordinates and the Head II X-ray coordinates illuminate various aspects of the maturation pathway in the course of which the pattern of inter-subunit interactions is sequentially transformed while the integrity of the capsid is maintained.
Bacteriophage capsid assembly pathways provide excellent model systems to study large-scale conformational changes and other mechanisms that regulate the formation of macromolecular complexes. These ...capsids are formed from proheads: relatively fragile precursor particles which mature by undergoing extensive remodeling. Phage HK97 employs novel features in its strategy for building capsids, including assembly without a scaffolding protein, and the formation of a network of covalent cross-links between neighboring subunits in the mature virion. In addition, proteolytic cleavage of the capsid protein from 42 kDa to 31 kDa is essential for maturation. To investigate the structural bases for proteolysis and cross-linking, we have used cryo-electron micrographs to reconstruct the three-dimensional structures of purified particles from four discrete stages in the assembly pathway: Prohead I, Prohead II, Head I and Head II. Prohead I has icosahedralT= 7 packing of blister-shaped pentamers and hexamers. The pentamers are 5-fold symmetric, but the hexamers exhibit an unusual departure from 6-fold symmetry, as if two trimers had undergone a shear dislocation of about 25 Å. Proteolytic conversion to Prohead II leaves the outer surface largely unchanged, but a major loss of density from the inner surface is observed, which we infer to represent the excision of the aminoterminal domains of the capsid protein. Upon expansion to the Head I state, the capsid becomes markedly larger, thinner walled, and more polyhedral: moreover, the capsomer shapes change radically; especially notable is the disappearance of the large hexon dislocation. No differences between Head I and the covalently cross-linked Head II could be observed at the current resolution of about 25 Å, from which we infer that it is the conformational rearrangements effected by expansion that create the micro-environments needed for the autocatalytic formation of the iso-dipeptide bonds found in the mature virions (“pseudo-active sites”).
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